1. Field of Invention
This invention relates to a peripheral multifunction device which can simultaneously execute a plurality of functions and which can serve in use as a peripheral device connected to information processing units such as personal computers.
2. Description of Related Art
Peripheral multifunction devices having a facsimile function, printer function and scanner function have recently been developed to serve as peripheral devices for information processing units such as personal computers. The peripheral multifunction device is constituted to be capable of simultaneously performing the three functions by multitasking. Each of the functions is accomplished in the peripheral multifunction device by transmitting and receiving to and from the information processing unit various data including printer data, scanner data, facsimile reception data and facsimile transmission data. Memories such as RAM or EEPROM need to be used for processing the various data. The above-described conventional peripheral multifunction device is provided with three memories dedicated to the three functions respectively so that the functions are simultaneously accomplished without interference with one another. However, since the three memories are provided for the respective functions, a capacity of each memory is increased and consequently, a production cost of the device is increased.
The inventor of the present application intended to reduce the capacity of each memory to a value as small as possible for the purpose of reducing the production cost. The inventor then designed a peripheral multifunction device in which a single memory was provided so as to be used commonly for the three functions and the capacity of the memory was reduced to a value as small as possible. The designed peripheral multifunction device has not been published yet.
The inventor has found several points to be improved in the designed constitution. More specifically, a large storage area is used in the peripheral multifunction device for the processing of a large quantity of compressed printer data when the printer data is transmitted from the information processing unit to the peripheral multifunction device, for example. The reason for this is that since a processing until the actual printing of the received printer data is slower than a processing of transmitting the printer data, the unprinted printer data tends to be successively accumulated in the memory. Accordingly, a remaining capacity of the memory is gradually reduced as additional printer data is transmitted. Further continued transmission of the printer data finally uses up the entire memory capacity, resulting in an system error. To prevent the memory from being full of stored data, the inventor constituted the peripheral multifunction device so that the data transmission and reception was inhibited between the information processing unit and the peripheral multifunction device by a hardware or software arrangement when the decrease in the memory remaining capacity to or below a predetermined value was detected.
In the above-described peripheral multifunction device, however, the data transmission and reception are completely inhibited between the information processing unit and the peripheral multifunction device when the memory remaining capacity has decreased to or below the predetermined value. Accordingly, the transmission and reception of facsimile data and scanner data each using a smaller memory capacity cannot be performed as well as that of the printer data using a larger memory capacity. In other words, a shortage in the memory remaining capacity interrupts the functions not resulting in full storage of the memory as well as the function resulting in full storage of the memory or printer function, namely, even the functions operable even when the remaining capacity of the memory becomes short are interrupted. Consequently, the efficiency in the use of the peripheral multifunction device is lowered, which results in a low usability of the device.